The invention relates generally to authentication systems and methods for digital images and more particularly to improved methods, systems and signals for authenticating digital images.
The use of digital images and videos by both consumers and professionals is pervasive. Accordingly, it has become important to provide a system and method for authenticating digital images and videos to insure that they have not been tampered with. As an example, an authentication system could insure that someone has not replaced a person""s face with that of another on a digital picture or series of video frames.
Authentication systems are known which extract a short signature from images (or video frames) which can be either inserted into the image signal or stored separately. The owner of the original content can use the signature to verify whether the content has been modified or users can confirm that they are receiving authentic digital images.
Conventional content-based image authentication systems typically define an image into many blocks and extract characteristics about the blocks. For example, the image can be broken up into 16xc3x9716 blocks as in FIG. 1 or some other number of blocks, and some characteristic about the block, such as average luminance or chrominance values with respect to R, G, B or gray values. The characteristics of adjacent pairs of blocks are commonly compared and a signature is extracted based on this comparison. For example, if the average luminance value for the red component of a first block 110 of an image 100 is greater than or equal to that of a second block 120, a one bit will be generated. Otherwise, a zero bit will be generated. The process is repeated with successive blocks until a binary signature of ones and zeros is compiled.
A disadvantage to this method is that because pairs of blocks each contribute a bit to the signature, it is possible to change the pair of blocks without affecting the signature by maintaining the difference or similarity of the compared characteristic of each block. It can be possible to reverse engineer the signature and then alter the image in such a manner to generate an identical signature and thus frustrate the authentication mechanism.
The following references discuss processing video signals, coding image blocks and authentication algorithms for digital images, the contents of which are incorporated herein by reference: WO 93/11502, U.S. Pat. No. 4,254,400, U.S. Pat. No. 5,351,095, U.S. Pat. No. 5,520,290 and U.S. Pat. No. 5,870,471.
Techniques for performing pair-wise block comparisons in a non-hierarchical technique are discussed in xe2x80x9cGenerating robust digital signature for image/video authenticationxe2x80x9d, C. Y. Lin and S. F. Chang, in Proceedings of Multimedia and Security Workshop at A. C. M. Multimedia, September 1998. Inserting and/or hiding a signature in an image signal is discussed in xe2x80x9cSecure spread spectrum water marking for images, audio and video,xe2x80x9d I. Cox, et al., in IEEE Int""l. Conf. on Image Processing, Vol. 3, pp. 243-246 (1996). The contents of these references are incorporated herein by reference.
Accordingly, it is desirable to provide an improved method and system for authenticating digital images which overcomes drawbacks of conventional methods and systems.
Generally speaking, in accordance with the invention, a method and system for creating authentication signatures for digital images is provided. The method and system involves partitioning the image into multiple blocks, comparing characteristics from each block and generating signature data bits based on the comparison. Each block can then be broken up into additional blocks and those blocks can be compared to create additional sets of signature bits which can be combined with the signature bits from the first set of blocks. Each or a portion of these new smaller blocks can be further broken up and the procedure can be repeated to provide an authentication signature of desired length by combining all or parts of the signature segments.
Accordingly, it is an object of the invention to provide an improved method and system for authenticating digital images and video.
Another object of the invention is to provide a method of creating an authentication signature for a digital image which is difficult to duplicate if the image is altered.
Another object of the invention is to provide an improved system for creating, storing and using authentication signatures for digital images which are difficult to duplicate if the original image is altered.
The invention accordingly comprises the several steps and relation of one or more of such steps with respect to each of the others and the product, system, signal and media adapted to effect or resulting from such steps, or as is exemplified in the following detailed description and drawings and the scope of the invention will be indicated in the claims.